import java.util.*;
import java.math.*;
public class juli{
  public static void main (String[]args){
    Scanner input=new Scanner(System.in);
    double x1=input.nextDouble();
     double y1=input.nextDouble();
      double x2=input.nextDouble();
       double y2=input.nextDouble();
       System.out.println(String.format("%.2f",Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2))));
    
  }
}
